Ignition distributor



Nov. 19 1968 R. A. SOETERS 3,412,222

IGNITION DISTRIBUTOR Filed Sept. 27, 1965 f 7'0 MA IFOLO mew/w INVENTOR. AJM/O/Vfl '4. $05 TERS ATTORNEY United States Patent 3,412,222 IGNITION DISTRIBUTOR Raymond A. Soeters, Royal Oak, Mich., assignor to Holle Carburetor Company, Warren, Mich., a corporation of Michigan Filed Sept. 27, 1965, Ser. No. 490,507 13 Claims. (Cl. 200-19) ABSTRACT OF THE DISCLOSURE An ignition distributor includes a housing, a shaft journalled in the housing, a movable ignition advance plate in the housing and preferably disposed at right angles to the axis of the shaft, the plate being pivotally mounted in the housing by means displaced from the axis of the shaft, means for causing movement of the plate in the plane thereof with respect to the shaft, the mounting means including means for permitting and causing a point on the plate to move'substantially in a circular are having the axis of the shaft as its center even though the plate is eccentrically mounted with respect to the shaft, whereby both the advantage of eccentric mounting and the uniform dwell angle advantage of concentric mounting of the advance plate are substantially obtained.

This invention relates to ignition distributors, and more particularly to a constant dwell spark advance mechanism for use in automotive type ignition distributors.

Most automotive ignition distributors include means whereby the spark timing can be varied as a function of some engine operating parameter such as manifold vacuum. At high vacuums, the spark timing is advanced; at lower vacuums, the spark timing is retarded. In a typical case, the spark advance mechanism includes a vacuum diaphragm assembly and link, a movable advance plate and a stationary plate, the vacuum diaphragm and link causing the advance plate to move in accordance with engine manifold vacuum. This, in turn, causes the breaker contact set, which is mounted on the movable advance plate, to move relative to the cam in such a way as to change the spark timing.

Various methods of mounting the advance plate in the distributor are employed, the two most common arrangements being the concentric type and the pivot type.

In the concentric type advance mechanism, an example of which is disclosed in Grant, 2,465,529, the advance plate rotates concentrically about the axis of the distributor shaft, and the cam formed thereon, as it is being moved to advance the spark, the concentric movement being usually provided by rotating the advance plate about a guide bearing mounted on the stationary plate. The advantage of this construction is that the rubbing block of the breaker contact set moves concentrically around'the cam so that the contacts are always opened to the same gap by the cam lobes acting on the rubbing block. This results in a constant dwell angle (the amount of angular rotation of the cam or time per cylinder during which the contacts remain closed) regardless of the degree of spark advance or retard. However, the disadvantages of the concentric structure is the expense of the guide bearing and associated parts, the diificulty of maintaining necessary tolerances and the eventual loss of accuracy due to wear.

3,412,222 Patented Nov. 19, 1968 The other popular spark advance structure is the pivot plate type, an example of which is shown by Frank,-

3,098,366. In this type of mechanism, the movable advance plate is pivoted about a point which does not lie on the axis of the cam. Because of this eccentric location of the pivot point, the rubbing block of the contact set moves along a path that is not concentric. This causes a variation in the extent of contact opening, and hence the dwell angle, depending upon the degree of spark advance. Such variation is objectionable because the optimum dwell angle cannot be maintained throughout the spark advance range. Despite this disadvantage, the pivot plate type structure is popular because it is, due to the simplicity of its component parts, less expensive than the concentric type mechanism.

From the above discussion, it is apparent that the concentric spark advance structure has the very definite advantage of providing a highly desirable constant dwell angle; however, this structure has certain disadvantages, as pointed out above. The pivot plate type structure has the obvious advantage of lesser cost, but it also has the serious disadvantage of a variable dwell angle.

Accordingly, a primary object of this invention is to provide distributor spark advance mechanism having the lesser cost advantage of the prior art pivot plate structure and, at the same time, the constant dwell angle advantage of the prior art concentric structure.

Another object of the invention is to provide such a structure that is easy to manufacture and assemble and is rugged and dependable in operation.

Still another object of the invention is to provide a distributor spark advance mechanism characterized by a pivot plate having a shifting pivot point, over the range of the spark advance required, resulting in the contact set rubbing block following a path that is concentric, or substantially concentric, with the axis of,the cam.

A still further object of the invention is to provide such a mechanism where the variation of the pivot point is provided by a simple cam mechanism means of cooperation between the advance plate and the stationary plate or other support member.

These and other objects and advantages of the invention will become more apparent upon reference to the following specification and the attached drawings wherein:

FIGURE 1 is a top plan view, with the distributor cap removed and with portions thereof cut away, of a distributor embodying the invention;

FIGURE 2 is a fragmentary cross-sectional view taken on the plane of line 22 of FIGURE 1, and looking in the direction of the arrows;

FIGURE 3 is a perspective view of the cam element shown in FIGURES l and 2;

FIGURE 4 is a plan view of the retainer spring shown in FIGURE 2.

Referring now to the drawings, a distributor 10 embodying the invention comprises an annular housing 12 in which a distributor shaft 14 having a multi-lobed cam 16 formed on or secured thereto is mounted, the shaft being driven by the engine so that the cam rotates in a counterclockwise direction as shown by the arrow. A stationary plate 18 is secured in the housing 12 in a posi tion perpendicular to the axis of the shaft 14 by any suitable means such as the screws 20, the plate having a central aperture 22 through which the cam 16 may pass.

The distributor also includes a movable spark ad- Vance plate 24, which is also provided with a similar central opening 26 through which the distributor cam may pass. The usual breaker contact set 28, which may be of any desired particular construction, is mounted on the movable spark advance plate 24 by means such as the screws 30 and 32, the base 34 of the contact set having a slot 36 for the screw 30 so as to provide for limited adjustment of the contact set on the advance late. P As is well known in the art, the movable contact arm 38 is mounted on a pivot 40 and is spring biased to keep the contacts 42 and 44 closed, and, as the cam 16 rotates, the lobes 46 thereof engage the rubbing block or cam follower 48 to intermittenly open the contacts.

To this point, the structure described is well known in the art, and, as will be seen by reference to the Grant and Frank patents, certain details of construction not necessary for an understanding of the invention have not been shown and described. As already stated, in the prior art the movable advance plate 24 is mounted either concentrically, as shown by Grant, or on an offset pivot, as shown by Frank. Movement of the plate 24 is effected by a rod or link 50 connected to an engine vacuum responsive device 52 which, due to the link connection between it and the movable advance plate, determines the position of the plate at any given time.

It is obvious that if the advance plate 24 were mounted concentrically, as in Grant, the center 54 of the rubbing block 48 would follow a path 55, during spark advance, that is concentric with the axis 56 of the cam 16. However, if the plate 24 is mounted on a pivot that is offset from the cam axis, as in Frank, the center 54 of the rubbing block will follow a path 58, during spark advance, that is not concentric with the cam.

The structural differences between the invention and the prior art will now be described. In this connection, it will be noted that the stationary plate 18 is formed with an opening 60 that is symmetrical with respect to its centerline XX, which also extends through the axis 56 of the cam 16, the functional features of the opening 60 being described below. The stationary plate is also formed with two additional spaced openings 62, one on each side of the opening 60.

The plate 24 has secured to the underside thereof what may be referred to as a rocker or cam block 64, attachment being by means such as the coined over stem 66 and spaced projections 68 to prevent relative movement between the rocker block 64 and the advance plate 24.

Referring now to the rocker block or cam 64, it will be seen that it has a generally semi-circular outer edge 70 with a recess to provide spaced projections 72 on opposite ends of a suitably curved edge or rocking surface 74. The securing stem 66 and the pins 68 extend from one flat surface of the block 64, and a pin 76 extends from the other side thereof, preferably on the same axis as the securing stem 66.

The movable advance plate 24 is assembled on the stationary plate 18 in a manner so that the cam block 64 is received in the opening 60 in the stationary plate, as shown in FIGURES 1 and 2; that is, the cam or rocking surface 74 is adjacent the straight line portion 78 of the opening 60, with the projections 72 on the cam' being received in the slots 80 formed in the edge of the opening 60 adjacent the cam 16. The dimensions of the cam block 64 and the opening 60 are such that the outer edges of the projections 72 slide along the side edges 82 of the opening 60 as the advance plate 24 is moved to advance or retard the spark.

A biasing spring 84 having a central curved portion 86 generally conforming to the semi-circular outer edge 70 of the cam 64 is provided with hooked portions 88 at each end thereof that engage the edges of the spaced openings 62. The spring 84 urges the cam 64 and advance 24 assembly plate upwardly in FIGURE 1 so that the cam surface 74 engages the straight line edge 78 of the opening 60.

The advance plate 24 is supported on the stationary plate 18, in parallel relation thereto, by any means such as the three nylon or other suitable blocks 90 which are generally equally spaced about the axis 56 of the cam and may be secured by any suitable means either in the movable plate 24, as shown in FIGURE 2, or in the stationary plate 18. A spring 92, which in this case is a bowed leaf spring but which may be of any suitable design, is secured at its center on the pin 76 extending from the bottom of the cam block 64, the spring being assembled so that the ends 94 thereof engage the underside of the stationary plate 18 and resiliently hold the stationary and movable plates in the desired parallel relation.

OPERATION With the above structure, it will be seen that a cam surface 74 on the rocker block 64 can be selected, either by trial and error or by mathematical computation, which will result in a shifting pivot point P for the movable plate 24 as it is rotated clockwise or counterclockwise by the link 50 connected to the vacuum diaphragm or other assembly 52.

In other words, as the advance plate 24 is moved, the rocker or cam block 64, which is always in contact with the straight line surface 78 of the opening 60 in the stationary plate, contact being maintained by the spring 84, rocks on its curved surface 74. The advance plate 24 does not move about a fixed pivot, as in the case of the structure shown by the Frank patent; rather, it rotates about a moving pivot point P, which is on the centerline of the rocker block 64 that also extends through the center 54 of the contact set rubbing block 48, in a manner so that the center 54 of the rubbing block follows a path 55 having a constant radius about the axis 56 of the cam 16.

Since the rubbing block remains at a fixed distance from the cam axis throughout the spark advance range, the amount of contact opening and the dwell angle also remain constant throughout this range. Another advantage of the advance mechanism of the invention is that there is no sliding of the surfaces 78 and 74; friction and wear are thus kept at a minimum.

It should also be apparent that the edge 78 of the opening 60 on which the contoured edge 74 of the cam block 64 rocks need not necessarily be a straight line edge; that is, it could also be a contoured or curved surface, depending upon the operating characteristics desired in the advance mechanism. Alternatively, the edge 74 of the rocker block 64 could be a straight line or some other shape, and the straight edge 78 of the opening 60 could be a curved or contoured surface. It is also apparent, as already stated, that the fixed plate 18 is not essential to the invention, since the surface 78 on which the cam block surface 74 rocks could be formed on some other stationary part of the distributor housing or other structure. Also, the cam block 64 need not necesarily be a separate piece; that is, the surface 74 could be formed on the movable plate 24.

The main feature of the invention is to provide a less expensive non-concentric type distributor advance mechanism which results in concentric, or substantially concentric, paths of the rubbing block over the range of spark advance, and the invention has been described in sufficient detail to enable anyone skilled in the art to practice the same.

While a preferred embodiment of the invention has been shown and described for purposes of illustration, other modifications may be possible within the scope of the invention, and no limitations are intended except as recited in the following claims.

What I claim as my invention is:

1. An ignition distributor having means to advance the spark, said distributor comprising, a housing, a shaft mounted axially in said housing, a multi-lobed cam on said shaft, a movable plate mounted in said housing perpendioular to the axis of said shaft, means for moving said plate, a set of breaker contacts mounted on said movable plate, said contacts having a cam follower engaged by the lobes of said cam to open and close said contacts, and means for mounting said movable plate, said mounting means being non-concentric with respect to the axis of said shaft but providing movement of a point on said movable plate during spark advance about a shiftable pivot in a manner so that said cam follower substantially traverses a path having the axis of said shaft as its center.

2. An ignition distributor having means to advance the spark, said distributor comprising a housing, a shaft mounted axially in said housing, a multi-lobed cam on said shaft, a movable plate mounted in said housing perpendicular to the axis of said shaft, means for moving said plate, a set of breaker contacts mounted on said movable plate, said contacts having a cam follower engaged by the lobes of said cam to open and close said contacts, and means for mounting said movable plate eccentrically with respect to the axis of said shaft in a manner to cause rotation and translation thereof in its plane such that said cam follower follows substantially a circular arc path having said axis of the shaft as its center throughout the spank advance range, said mounting means including contact between a fixed surface in said housing and a moving surface on said movable plate, at least one of said surfaces being nonlinear.

3. Structure as recited in claim 2 and having, in addition, means for preventing translational movement of said movable plate in at least one direction.

4. Structure as recited in claim 2 and having, in addition, resilient means for maintaining said surfaces in engagement.

5. An ignition distributor, comprising a cylindrical housing, a shaft mounted axially in said housing, a multilobed cam on said shaft, a stationary plate fixed in said housing perpendicular to the axis of said shaft, a first opening formed in said stationary plate, said opening having a straight line edge on the cam side thereof, said opening being symmetrical about its centerline which also passes through the center of the cam, said straight line edge being perpendicular to said centerline, second openings in said stationary plate, one on each side of said first opening, an eccentrically mounted movable plate in said housing positioned adjacent to said shaft, a set of ignition contacts mounted on said movable plate, said contacts including a movable contact arm having a cam follower adapted to be engaged by the lobes of said cam to open and close said contacts, means for moving said movable plate, means for maintaining said plates parallel to one another, means for resiliently clamping said plates together, said movable plate having a cam member on the side thereof adjacent said fixed plate, said cam member being received in said first opening and having a cam edge adjacent said straight line edge of said first opening, and resilient means urging said cam edge against said straight line edge, whereby co-operation between said cam edge and said straight line edge controls movement of said movable plate in a manner so that said cam follower moves in a path substantially concentric with the axis of said cam.

6. An ignition distributor, comprising a housing, a shaft mounted axially in said housing, said shaft having a multi-lobed cam thereon, a movable plate in said housing extending perpendicular to and mounted eccentrically with respect to the axis of said shaft, a set of ignition contacts mounted on said movable plate, said contacts having a cam follower adapted to be engaged by the lobes of said cam to open and close said contacts, a cam surface formed on said movable plate, a stationary surface in said housing with which said cam surface may co-operate, means for anchoring said movable plate so that said surfaces are in engagement, means for moving said movobl'e plate, said cam surface resulting in said cam follower moving substantially in a circular arc path with the axis of said cam as its center.

7. An ignition distributor, comprising a rotatable shaft, a spark advance mechanism including a movable plate, means for moving said plate and means for mounting said movable plate so as to provide a shiftable pivot point that is offset from the axis of said shaft but so that a point on said plate moves in a substantially circular arc path having the axis of said shaft as its center.

8. An ignition distributor such as that recited in claim 7, 'wherein said means for mounting said movable plate ineludes two surfaces in contact, one of said surfaces being formed on said plate .and at least one of said surfaces being a curved surface.

9. An ignition distributor, comprising a housing, a shaft having a multi-lobed cam mounted axially in the housing, a set of breaker contacts opened and closed by engagement with said cam, means for repositioning said contacts with respect to said cam so as to advance and retard the spark, said repositioning means including means eccentric with respect to the axis of said cam for mounting said contacts for movement of the point of engagement thereof with said cam in a substantially circular arc with respect to said cam axis.

10. An ignition distributor comprising breaker contacts having a follower engaging a multi-lobed cam, means for providing a spar-k advance mechanism in which said follower moves in a substantially circular arc having the axis of said cam as its center but in which the axis of said cam as its center but in which the axis of rotation of said follower is displaced from the axis of said cam, and means for preventing translational movement of said follower in at least one direction.

11. A distributor, comprising a housing, a shaft mounted axially in said housing, a multi-lobed cam on said shaft, a stationary plate fixed in said housing perpendicular to said shaft, an opening in said plate having the centerline thereof passing through the axis of said shaft and a straight edge perpendicular to said centerline, a movable plate parallel to said stationary plate, a set of breaker contacts, fixed on said movable plate and having a cam follower to be engaged by said cam lobes, a cam edge formed on said movable plate, said cam edge being held in rolling engagement with said straight edge by resilient means, the centerline of said cam edge passing through the centerline of said cam follower, and means for moving said movable plate, said rolling engagement resulting in pivoting of said movable plate about a shifting axis offset from the axis of said multi-lobed cam but in movement of said cam follower in a substantially circular arc path having the axis of said cam as its center.

12. An ignition distributor, comprising a housing, a shaft journalled in said housing, a movable ignition advance plate in said housing and disposed at right angles to the axis of said shaft, said plate being mounted in said housing by means eccentric with respect to the axis of said shaft, means for causing movement of said plate in the plane thereof with respect to said shaft, said mounting means including means for permitting and causing a point on said plate to move substantially in a circle arc having the axis of the shaft as its center.

13. An ignition distributor, comprising a housing, a shaft journalled axially in said housing, a support plate fixed in said housing and positioned at right angles to the axis of said shaft, a second movable plate positioned parallel to said fixed plate, means eccentric with respect to the axis of said shaft for securing said movable plate in a manner to permit movement thereof in its plane, said securing means including means for preventing translational movement of said movable plate in respect to said fixed plate in one direction but permitting rotational point on said movable plate substantially along the arc 7 i 8 movement and translational movement in a direction 'References Cited normal to the prevented translational movement of said UNITED STATES PATENTS movable plate with respect to sald fixed plate, means pivotally secured to said movable plate for moving said 4/1965 McCarty 200-19 3,242,274 3/1966 Sander 200-31 movable plate by the application of a force tangential to 5 h 52.1 shaft, said force resulting in t e movement of a BERNARD A. GILHEANY Primary Examiner.

of a circle having the axis of said shaft as its center. H. BROOME, Assistant Examiner. 

